As is different from conventional silver halide light sensitive photographic materials, there is no fixing process after development in thermally developable photosensitive materials. In the thermally developable photosensitive materials, there are, however, problems such that silver image tone easily varies. Recently, as a light source used for the thermally developable photosensitive materials are employed a laser light source at wavelengths in the infrared region due to its high energy and low price. In response thereto are employed thermally developable photosensitive materials which are spectrally sensitized with an infrared sensitizing dye. It has been commonly known that infrared-sensitizing dyes are inferior in adsorption to silver halide, as compared to visible region-sensitizing dyes, producing problems such as low sensitivity or marked reduction in sensitivity following pre-exposure storage. A technique of using an infrared sensitizing dye is disclosed in JP-A 5-66515 (hereinafter, the term, JP-A means an unexamined and published Japanese Patent Application). This technique, however, does not address any thermally developable photosensitive material and is not directed to solving problems such as reduction in sensitivity during pre-exposure storage or variation of silver image tone after development of thermally developable photosensitive materials. Binders used in thermally developable photosensitive materials are different from those used in conventional silver halide photographic materials, and therefore adsorption of spectrally sensitizing dyes used in the thermally developable photosensitive materials are also different from binder matrix of gelatin in the conventional silver halide photographic materials. Further, the thermally developable photosensitive material is added with an organic silver salt, a reducing agent and a silver cluster-bleaching agent which also exhibits antifogging function or an acid capable of adjusting thermal development. However, there has not been developed a means for improving silver image tone or pre-exposure storage stability, without deteriorating the function of such addenda.